Inhibitors of apoptosis proteins (IAPs) are intracellular proteins, with important roles in regulating cell death, inflammation, and immunity. Here, we examined the clinical and therapeutic relevance of IAPs in colorectal cancer. We found that elevated expression of cIAP1 and cIAP2 (but not XIAP) significantly correlated with poor prognosis in patients with microsatellite stable (MSS) stage III colorectal cancer treated with 5-fluorouracil (5FU)-based adjuvant chemotherapy, suggesting their involvement in promoting chemoresistance. A novel IAP antagonist tolinapant (ASTX660) potently and rapidly downregulated cIAP1 in colorectal cancer models, demonstrating its robust on-target efficacy. In cells co-cultured with TNFα to mimic an inflammatory tumor microenvironment, tolinapant induced caspase-8-dependent apoptosis in colorectal cancer cell line models; however, the extent of apoptosis was limited because of inhibition by the caspase-8 paralogs FLIP and, unexpectedly, caspase-10. Importantly, tolinapant-induced apoptosis was augmented by FOLFOX in human colorectal cancer and murine organoid models in vitro and in vivo, due (at least in part) to FOLFOX-induced downregulation of class I histone deacetylases (HDAC), leading to acetylation of the FLIP-binding partner Ku70 and downregulation of FLIP. Moreover, the effects of FOLFOX could be phenocopied using the clinically relevant class I HDAC inhibitor, entinostat, which also induced acetylation of Ku70 and FLIP downregulation. Further analyses revealed that caspase-8 knockout RIPK3-positive colorectal cancer models were sensitive to tolinapant-induced necroptosis, an effect that could be exploited in caspase-8-proficient models using the clinically relevant caspase inhibitor emricasan. Our study provides evidence for immediate clinical exploration of tolinapant in combination with FOLFOX in poor prognosis MSS colorectal cancer with elevated cIAP1/2 expression.
Bibliographical noteFunding Information:
J.M. Munck reports personal fees from Astex Pharmaceuticals outside the submitted work. M. Lawler reports grants from Pfizer; personal fees from EMD Serono, Roche, BMS, and Carnall Farrar outside the submitted work. V.M. Coyle reports nonfinancial support from Astex Pharmaceuticals during the conduct of the study; personal fees from Servier and other support from Servier outside the submitted work. D.B. Longley reports grants from Astex Pharmaceuticals during the conduct of the study. No disclosures were reported by the other authors.
This work was supported by a studentship (K.J. Stott) sponsored by The Northern Ireland Department for the Economy (NI DfE), and by funding from a CRUK Program grant (D.B. Longley/S.S. McDade) C11884/A24367, a CRUK Experimental Cancer Medicine Centre (ECMC) program grant, (V.M. Coyle/D.B. Longley) C36697/A25176, a Northern Ireland Health and Social Care Research and Development award (V.M. Coyle/D.B. Longley/C. Latimer) COM/5535/19, a CRUK Career Development Fellowship (E.M. Kerr/W. McDaid) C61288/A26045. Additional support (D.B. Longley, C. McCann) was obtained from NI DfE (SFI-DEL 14/1A/2582 and STL/5715/15 - US-Ireland Partnership). T. Sessler and M. Lawler were supported by an HDR-UK grant (JHR1157-100/1230). D.B. Longley was also in receipt of direct funding from Astex Pharmaceuticals.
© 2021 The Authors; Published by the American Association for Cancer Research
ASJC Scopus subject areas
- Cancer Research